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The preterite tense (or pretérito perfecto) refers to an event that occurred once in the past, whereas the imperfect tense (pretérito imperfecto) refers to an event that occurred continuously or more than...

Originally, 1/5 of 20 marbles are red. 1/5 of 20 = 4. If i add 1 more we have 5 red marbles. 5/20 = 1/4.

When writing a history essay the basic structure that you learnt at GCSE can be employed at A-Level: Introduction - Point 1- Point 2 - Point 3 - Conclusion. However, when writing at A-Level standard new c...

We will use integration by substitution to solve this integral.

Let 1-x^2=sin^2(u)

This means that:

x^2=1-sin^2(u)=cos^2(u) (using the trigonometric identity sin^2(x)+cos^2(x)=1). The...

First, we need to try and eliminate one of the x or the y variables from both equations. Here, we are going to eliminate the y variable. In order to do this, we need to make the y coefficients equal in bo...